Total system efficiency is key

Trane specialist calls for holistic approach to energy savings

Jonathan Spreeman.
Jonathan Spreeman.

Trane specialist calls for holistic approach to energy savings

Manufacturing more efficient chillers is not the ultimate solution to achieve maximum energy savings. “A lot of people tell us as a manufacturer that if we just produce more efficient chillers, they will have more efficient plants.

“However, at the rate we are progressing in terms of chiller efficiency, we are getting closer and closer to those theoretical maximum efficiencies. So we need to start looking at a more holistic view, and look at the entire plant,” said Trane chiller systems specialist Jonathan Spreeman at the IDEA district cooling conference and exhibition in Dubai.

Spreeman said that system optimisation was currently a major focus. “This is due to the necessity for energy efficiency, which is obviously a major concern. The focus on this has been partly deflected by the economic crisis.

“If you recall, prior to the current economic downturn, the focus was very much on energy and skyrocketing oil prices. Now there has been a kind of a switch and optimisation is being looked at again, especially with such concepts as the ‘smart grid’.

“By being able to design systems upfront that consume less energy, you are going to lower your energy demand automatically. This makes for a very powerful tool. There is a lot of talk about implementing ice thermal storage, for example.

If you can get to the point where you are designing systems almost intuitively in terms of maximum efficiency, then additional factors such as chilled water storage will have an even greater effect on your overall system.

“How do we adapt to this new milieu? How do we ensure that our equipment and systems are ready for it? The emphasis has to be on the initial system design. Energy inefficiency is not something you can fix retroactively through ice thermal storage, for example. Proper plant design upfront can help tremendously,” argues Spreeman.

“The speed of light is roughly 300 million metres a second. In the HVAC industry, we move a bit slower: two metres per second for water, and ten to twenty metres per second for air. While we do not move very fast, we move vast quantities.

Take for example a 10 000 TR chiller, which moves roughly 6.8 million pounds/hour of air and roughly 14.4 million pounds of water.” This implies there is considerable scope for system optimisation. Spreeman says there are certain obvious things that can be done:

  • Colder chilled water reduces energy consumption (chilled water pumps);
  • Warm condenser water reduces energy consumption (condenser water pumps);
  • Cooling tower control reduces energy consumption (cooling tower fans).

Series chillers also promote energy efficiency. “Series-series chillers in counterflow are very common in Dubai. When you start talking about smart grids and demand response, these will result in a roughly 20% energy saving on a base system.” Spreeman adds that advances in chiller controls have also allowed such concepts as variable primary flow to enter the mainstream.

“We have progressed from pneumatic controls in the 1960s to 1980s, analogue controls in the 1980s to 1990s, to digital controls today.

This means that equipment can now ‘talk’ to each other, which helps to optimise a system. The other significant progress has been the move from sequence-driven controls to state-driven controls. This has proven to be very important.

“In the past we could only confirm one item at a time, such as evaporator water flow. Then we could we move onto the next item, such as condenser water flow. Only once all this had been done in a certain sequence could we start the chiller.

With state-driven controls, we can do many things at once. This is critical in terms of reliability, especially for mission-critical facilities, where restart time is an issue.”

Even though the Dubai district cooling sector has developed on a scale unprecedented in the rest of the world, Spreeman says it is still confronted with the same problems and trends as encountered elsewhere in the world.

“The sector here is obviously on a different scale than anywhere else. The magnitude is incredible; it really is mind-boggling. Larger chiller plants in the US are ten times smaller than some of the ones here.

“But the issues are still the same. Everyone still wants to reduce energy consumption. ASHRAE is making a big push in this regard with its campaign to achieve net zero buildings by 2030. LEED is also driving a lot of energy efficiency measures and targets in this regard.

“It is because of such initiatives due to the energy crisis that people are now considering things they would not have considered before, such as ice thermal storage and future energy pricing,” concludes Spreeman.

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